I feel a great deal of pitching is muscle memory, and obviously each pitcher is different. That being said, I would never be looking anywhere but the glove once my body is moving to the plate. I always tell pitchers to focus on something small on the mit ( a string, a word, a letter). This makes the margin of error smaller. To me, looking at the glove is habit, and some pitchers have just grown bad habits over the course of their childhood.